http://physicsweb.org/article/world/15/9/6.
Two infinitely large parallel plates are attracted to each other by the CasimirEffect. At very small distances, in a vacuum, using optically flat conductors, this attractive force greatly exceeds more familiar forces such as gravity; it varies with the fourth power of distance.
They're attracted because the space between them doesn't allow virtual particles with wavelengths longer than the space between them, whereas the spaces outside allow virtual particles of all wavelengths. The attraction is just inwards pressure due to a partial real vacuum of virtual particles.
Spinoff conversations moved to ExplanationsInPhysics
Questions from someone who does not consider this math "trivial":
- How can optically flat conductors be maintained over such a "large" diameter?
- What is a virtual particle?
- What does it mean for a virtual particle to have a wavelength?
- Why can't virtual particles with wavelengths longer than the gap exist in the gap?
- What does the word "real" mean in "partial real vacuum"?
In reverse order,
- by "real vacuum" we refer to the absence of everything, as opposed to what we're stuck with under our laws of physics; a writhing mass of virtual particles and energy.
- Why can't a 5 metre long object exist in a breadbox?
- What does it mean for a real particle to have a wavelength?
- It's a particle that isn't real. Okay, okay. :) That's actually a good question and I don't like the standard pat answer so ... a virtual particle is one whose existence can't be detected directly because it doesn't carry any information. This is because it doesn't have enough energy or lifetime behind it. If it gets enough energy from a real particle, the virtual particle becomes real and vice versa.
- They can't. The Casimir effect is pretty much irrelevant except as a curiosity.
There is no math involved in understanding the Casimir effect. You just have to understand basic wave mechanics, the nature of the vacuum with its virtual particles, and that particles are waves.
More questions:
- How can something that "doesn't carry any information" produce a measurable force?
- Is this the result of an incomplete definition of information? (Similar to how many physicists say "A photon has no mass" when they really mean "A photon has no rest mass.")
- Or is the information content of the virtual particles automatically counted as part of certain real particles?
The Casimir effect, which is relatively easy to detect with modern experimental techniques is relevant since it demonstrates nicely the validity of "basic wave mechanics, the nature of the vacuum with its virtual particles, and that particles are waves".
Particles are waves was more than amply demonstrated by Huygens back in the 17th century. Since then, it has been redemonstrated again and again and again and again and again and again. And probably the most elegant of these demonstrations is the double slit / single photon experiment, which is not "relatively" easy but so easy as to be a cheap parlor trick. I admit the Casimir effect is a nice demonstration of the nature of the vacuum, but personally I much prefer quark confinement.
It is also relevant as though an obscure phenomenon it points the way to potential (pardon the pun) quantum leaps in space propulsion capability - http://www.daviddarling.info/encyclopedia/C/Casimir.html :
-
- This may be relevant to space travel because the region inside a Casimir cavity has negative energy density. Zero energy density, by definition, is the energy density of normal " empty space." Since the energy density between the conductors of a Casimir cavity is less than normal, it must be negative. Regions of negative energy density are thought to be essential to a number of hypothetical faster-than-light propulsion schemes, including stable wormholes and the Alcubierre Warp Drive.
For people who need subatomic particles sent somewhere fast. Actually, that could be useful, just not for propulsion...
CategoryPhysics, JustRevealsEssence
Casimir Effect